1. Field
One or more embodiments relate to a positive active material, a method of preparing the same, and a lithium secondary battery including the positive active material.
2. Description of the Related Technology
Lithium batteries are a type of secondary batteries that generate electricity by migration of lithium ions between positive and negative electrodes. Lithium secondary batteries typically include positive and negative electrodes, an electrolyte membrane, and a separator. Positive and negative active materials for the positive and negative electrodes may have structures allowing for reversible intercalation and deintercalation of lithium ions to enable lithium batteries to be charged and discharged by the reversible reactions.
Lithium batteries have been widely adopted, along with rapid increase in demand for portable devices such as mobile phones, personal digital assistants (PDAs), and laptop computers, even in the electric vehicle sector. In addition, demand for high-energy density lithium batteries is significantly increasing as the lithium batteries are increasingly miniaturized and having higher performance. While technologies of lithium batteries have been remarkably developed, better performance is still desired. For lithium secondary batteries, various kinds of carbonaceous materials are mostly used for negative electrodes and lithium composite oxides with various metals are mostly used for positive electrodes.
Energy of a lithium secondary battery is mainly dependant on a positive active material thereof. Commercially available small-sized lithium secondary batteries typically use a layer compound of LiCoO2 in a positive electrode thereof and carbon in a negative electrode thereof. LiCoO2 is a material having stable charge/discharge characteristics, good electronic conductivity, high thermal stability, and flat discharge voltage characteristics. However, the reserves of Co are small worldwide, and Co is expensive and toxic to the human body, and thus there is demand for alternative positive materials.
Currently, LiNiO2 and LiCoxNi1-xO2 have been actively researched and developed as positive electrode materials. However, LiNiO2 is difficult to commercialize due to difficulty in synthesis thereof and its poor thermal stability. LiCoxNi1-xO2 also does not have good performance to replace LiCoO2.
Thus, lithium secondary batteries including these positive active materials may have lifetimes that rapidly reduce with repeating charge and discharge. This is attributed to decomposition of electrolytes or deterioration of active materials caused by moisture inside the batteries or other factors, which subsequently increases internal resistance of the batteries. The present embodiments overcome the above problems and provide additional advantages as well.